H1 insulation rules: what changes on 27 November 2026

The transition period for New Zealand's updated insulation rules ends on 26 November 2026. From 27 November, every building consent application for a new home must show compliance with the 6th edition of H1/AS1, not the 5th. If you're designing or pricing a build now, here's what that means.

The short version

MBIE says the overall level of insulation required hasn't changed. What has changed is how you prove it:

• No more schedule method. The table of minimum R-values that many designers relied on has been removed. Compliance is now shown with the calculation method or the modelling method.
• Framing is counted more honestly. Wall R-values must be worked out assuming at least 38% of the wall is framing, unless you can show a lower figure.
• Areas are measured from the inside, using overall internal dimensions for roofs, walls and floors.
• Slab-on-ground floors lose their separate minimum R-value in the calculation method, though the slab still counts in the overall heat loss.
• Better tables for windows and slabs cover more common situations.

Why the 38% framing rule matters

Timber is a poor insulator. Every stud, nog, plate and lintel is a path for heat to bypass the insulation beside it. Under the old approach many wall calculations assumed less framing than real walls have. Now a framing fraction of 38% is the default.

Here's a rough comparison for a 90mm timber-framed wall, looking at the insulation layer only. It's a simple area-weighted estimate for illustration, not a compliance calculation, and treats 90mm of timber as about R0.75.

Wall build-up (90mm studs, 38% framing)	Approx. R-value of the insulation layer
R2.2 glass wool batts between studs	R1.3
R2.8 glass wool batts between studs	R1.4
R4.05 PIR (90mm) between studs	R1.5
R2.8 batts between studs + 25mm PIR (R1.10) over the frame	R2.5
R2.8 batts between studs + 40mm PIR (R1.80) over the frame	R3.2

Two things stand out. First, whatever you put between the studs, the framing drags the result down to around R1.3–R1.5. Second, a continuous layer over the frame isn't interrupted by timber, so its full R-value adds straight on. Just 25mm of PIR over the framing lifts the insulation layer by roughly 80%.

Your designer will do the full calculation to NZS 4214, including linings, air gaps and cladding, and the numbers will differ. But the pattern holds: under the new rules, the cheapest R-value in a wall is often a thin continuous layer outside the frame.

What this means for different projects

• Standard 90mm walls: batts alone may struggle in colder zones once 38% framing is applied. Options are 140mm framing, fewer studs where the engineering allows, or a continuous rigid layer.
• Renovations and reclads: a reclad is a good time to add PIR over the existing frame; see our drawing for exterior insulation to an existing wall.
• Tight spaces: where you can't make the wall thicker, a higher R-value per millimetre matters. Eurothane GP gives R4.05 in 90mm, against R2.8 for the best 90mm glass wool batt.

What to do before 27 November

1. Check which edition your drawings use. A consent lodged on or after 27 November must use the 6th.
2. Ask your designer to rerun the wall calculation with 38% framing.
3. If walls come up short, price a continuous PIR layer against 140mm framing before redesigning.

Specifying for a project? Call us on 03 540 3003 or send us your plans and we'll help you choose thicknesses. See the price list; we supply anywhere in NZ with freight quoted on each order.

See also: NZ Building Code insulation requirements

This article is a general guide, not design advice. For the full requirements see MBIE's H1 page.